The present invention relates to apparatus and methods for recording a three-dimensional illusion and more specifically for recording images for truly autostereoscopic display.
Production of two-dimensional images which may be used to provide a "true" three-dimensional illusion is a long outstanding goal in the visual arts field. The term "three-dimensional" has been expanded over the last several years by the computer imaging industry to include images produced using depth cues that take advantage of perspective, shading, reflections, and motion. Although, these images can be rendered with incredible results, they are nevertheless two-dimensional. A "true" three-dimensional image contains parallax information in addition to other two-dimensional depth cues.
Nature has given humans binocular vision, endowing them with two eyes which look in the same direction and whose visual fields overlap. Each of the eyes views the scene from a slightly different angle. The scene viewed is focused by the eye's lens on the retina. The retina is a concave surface at the back of the eye, lined with nerve cells, or nuerons. Since the surfaces of the retina are concave, the two images focused by the eye's are two-dimensional. Both two-dimensional images are transmitted by electrical impulses along the optic nerve to the brain's visual cortex. It is in the visual cortex that the two images are combined (fused), through stereopsis, to form a cyclopean view of the scene being observed by the two eyes. The brain is thought of as having a one-eyed or cyclopean eyed view of the world. That is to say, the ability to determine direction and see in three-dimensions, is something the individual eyes can not accomplish alone.
There is some question as to whether this cyclopean view is created by simultaneous processing of left and right views or a replacement phenomena in which a short-term memory buffer is used by the brain to compare left and right views.
Not all people with binocular vision can perceive three-dimensional images. From 2 to 10 percent of the population may fail to experience stereopsis in their day-to-day lives. Another 10 percent may achieve only limited stereopsis. It has been shown that stereoscopic vision differs greatly among individual people and that some practice is involved.
It has been observed that left and right eye information can be presented alternately to the left and right eyes, resulting in depth perception as long as the time interval does not exceed 100 ms. More recently, it has been demonstrated that stereoscopic information can be perceived by one eye if presented in the proper manner and it is possible for the brain to process and accept alternating parallax information, without regard to the direction of the parallax, from both eyes using a standard television screen.
Although humans are anatomically and psychologically capable of viewing the world around them in three-dimensions, they do not have the natural ability for depth perception on a two-dimensional screen, such as those used in motion pictures or television. The depth perceived on a two-dimensional screen is read into the image by viewers through a learned process based on their cultural and sociological backgrounds.
A great deal of effort has been devoted to developing three-dimensional display hardware. The two main categories for display hardware are, stereoscopic and autostereoscopic. Stereoscopic techniques require the viewer to wear some sort of apparatus to force each of the viewer's eyes to see a different perspective of the image. This group includes stereoscopes, polarization, anaglyphic, chromo-sterescopic, Pulfrich, and shuttering technologies. Autostereoscopic displays do not require viewing devices. Autostereoscopic display, including, among others, holography, lenticular screens, parallax barriers, and alternating pairs do not require the viewer to wear devices, but do require optical modifying display devices. True autostereoscopic display require no special display device. The development of autostereoscopic methods and techniques has to some extent paralleled development in the field of physiology of depth perception.
An example of a typical true autostereoscopic approach using horizontally displaced points of origin is described in U.S. Pat. No. 4,006,291 issued to Imsand in which images from one point of origin are primarily used while images from another point of origin are periodically inserted. Examples of non-horizontal systems are disclosed in U.S. Pat. No. 4,420,230 issued to McElveen, in which left and right images are diagonally separated and alternately displayed on a viewing surface at a rate determined by the distance to the nearest non-moving object. U.S. Pat. No. 4,429,328 issued to Jones, Jr., et al., shows a method for creating a three-dimensional effect by alternately displaying images from a pair of vertically displaced points of origin at a rate of 4 to 30 changes per second.
A principle drawback of alternating images from two viewing points, whether using horizontal, diagonal or vertical displacement approaches, is that slow moving or stationary objects in the scene being viewed tend to move or rock as the point of origin alternates. This image instability (rocking) phenomenon is attributable to the different viewing angles corresponding to the respective points of origin.
Image instability is the main reason why none of the above mentioned patents has been used or demonstrated commercially. Jones, Jr., attempted to control the rocking motion in U.S. Pat. No. 4,567,513 by adding a video mixing device, which intermittently superimposed the second point of origin onto the first point of origin at a rate of 4 to 30 times a second, rather than alternating images as before. This did little to control rocking and resulted in intermittent image softening.
The present inventors disclosed in U.S. Pat. No. 4,815,819 methods and apparatus for displaying a stable three-dimensional illusion. This approach relies on discrete motion between the various depth planes in a given scene. The motion is accomplished by two cameras (only one is need for stop-motion) critically aligned and manipulated throughout the entire filming or taping of a scene. By alternating the camera's images at a rate of between 1 to 60 changes per second and constantly keeping the discrete motion in balance, the resulting display is perceived by the viewer as having depth without a rocking motion.
While the U.S. Pat. No. 4,815,819 methods produce a stable three-dimensional illusion, they still require two cameras (two points of origin). A two camera system requires careful camera alignment to eliminate unwanted movement in all depth planes, precision matching of chrominance and luminance, accurate matching of camera tube scannings, and matching of lenses in focal length. Two camera systems tend to be large and heavy because of the additional optical elements in the folded optical path and the mount which is used to manipulate the cameras. Further, the optical path significantly reduces the light going to the cameras and prohibits short focal length lenses. Zoom and anamorphic lenses are more difficult to adapt to a two camera system. Zoom lenses require precision matching and tracking throughout their entire focal and zoom ranges. Exposure and focus changes are problem because of mechanical "slop" differences in the two lenses.
Therefore, it is an object of the present invention to provide a method for recording and creating a three-dimensional illusion using a single image receiver, be it real or simulated by computer or motion control. The use of a single image receiver removes all of the matching problems associated with a two camera method and practically allows the use of varifocal length (zoom) lens.
A further object of this invention is a method of blurring the background to enhance image stability without blurring the foreground.
Another object to this invention is a method of changing the view of the image receiver at a rate which is not closely related to the image recording rate.
Still another object of this invention is to provide apparatus for moving the image receiver or for manipulating the optical axis to simulate a moving image receiver.
A further object of this invention is to provide an additional depth cue by blurring the background.
Still another object of the invention is to provide a method of recording images for true autostereoscopic display with stable images.
The method and apparatus includes substantially continuously changing the view of a single image receiver substantially aligned to a convergent point in a scene along a scanning path and recording a plurality of scanning images for each cycle of traversing the scanning path. The optical length of views along the scanning path to the convergence point is substantially constant to maintain an object at the convergence point substantially motionless during recording of the plural scanning images. The scanning path is sufficiently short and the scanning rate is sufficient to produce motion, when displayed, which is within visio-psychological memory rate range. The scanning path may be an arc equidistant and centered on the convergence point and the image receiver is moved along rails tangent to the arc. The scanning path can also be an line segment sufficiently short such that all points along the line segment are substantially equidistant from the convergence point. For the line segment path, the image receiver is rotated simultaneous with moving along the scanning path for maintaining the objects at the convergence point substantially motionless.
The single image receiver and the scene may be moved relative to each other along the scanning path by: (A) moving the image receiver along the scanning path; (B) moving objects in the scene relative to the image receiver or (C) optically manipulating the optical path between the image receiver and the scene. In any of these methods of moving the single image receiver and the scene relative to each other, the frequency of recording the scanning image is independent of the rate of movement along the scanning path. The exposure time of the image receiver is set sufficiently along to produce the blurring of the objects in the scene not at the convergence point to enhance the effect. The scanning path and convergence point are variable.
As an alternative, the same effect may be achieved by producing a plurality of images in a fixed medium from different views along the scanning path and optically recording the fixed mediums. As another alternative, a computer is used to generate a plurality of images at the various points of view along the scanning path and storing them for ultimate display.
The apparatus for performing the method includes a single image receiver and a scanning apparatus for moving the optical axis of the image receiver and a scene relative to each other along a scanning path while maintaining the image receiver's optical axis substantially on a convergence point in the scene. A control is provided for actuating the image receiver to record a plurality of scanning images, greater than 2, for each cycle of traversing of the scanning path so as to have a scanning motion. The scanning apparatus defines the scanning path as an arc or a short line segment. If a short line segment defines the scanning path, the recorder is rotated simultaneously with movement along the scanning path. The scanning apparatus may include a carriage mounted to a pair of rails which moves the image receiver along the scanning path or moves objects in the scene relative to a fix image receiver. Also the scanning apparatus may optically manipulate the optical path to produce the scanning motion. The actuating device actuates the image receiver for exposure time sufficiently long to produce a blurring of the objects in the scene not at the convergence point. The actuating device activates the image receiver at a frequency independent of the rate of the scanning. The rate of movement is adjustable. The actuation frequency and the rate of movement of the scanning apparatus produce a motion of objects in the scene, when viewed, within the visio-psychological memory rate range. The scanning apparatus has the ability of changing the convergence point as well as the scanning path.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.